Are you running an alternator or a generator? The fuse link needs to be able to handle the highest battery charging current that's available from the charging system after startup, if you're running a standard wiring harness with the charging current going through the ammeter. I've seen short current surges of 80-100 amps from some alternators after a long cranking session. If you have a separate charging wire from the alternator to the battery, no problem, but the ammeter won't work right. Use a 50 amp fuse link, but be prepared to go bigger if it burns out from high alternator current.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!